The purpose of this study was to investigate the hypothesis that a protective mechanism of salivary antibody may be via interference with the glucose uptake system of acidogenic bacteria such as S. mutans. The effect of antisera to whole cells or cell wall components on glucose uptake by S. mutans 67l5 was examined. Stationary phase 67l5 cells were treated with test serum and incubated at 37 degrees C in the presence of 14-C -glucose. Samples were removed at timed intervals and measured in a liquid scintillation counter for radio-active uptake. Antisera to both whole cells and components known to be present on the surface of the cells reduced glucose uptake relative to normal serum.